The invention concerns a process for producing a film element having mutually registered metallic layers and such a film element.
Film elements with metallic reflection layers are frequently used to make it difficult and if possible prevent copying and misuse of documents such as banknotes, credit cards or charge cards or products, as an optically variable security element (OVD). To further increase the forgery-resistant nature of such film elements the use of optically variable security elements has been proposed, whose metallic reflection layer is not provided over the full area in the film element but is structured and is only partially provided in the film element. In that respect the expression mutually registered metallic layers is used to denote layers which are arranged in accurate register relationship with each other, that is to say which are structured in a fixed relationship with each other.
Thus for example WO 03/095227 A1 describes an optically variable security element whose metallic reflection layer is only partially provided and thus a transparent window is provided in the security element. In that respect, for structuring of the metallic reflection layer, it is proposed that the metallic reflection layer is vapour-deposited over the full surface area and then removed again by means of positive or negative etching or ablation in the regions in which the transparent window is provided.
It has now been found that further interesting optically variable effects can be achieved by a procedure whereby not just one metallic reflection layer is provided within a film element, but two partially shaped metallic reflection layers which appear opaque to the human viewer. In that case, particular significance is attributed to orientation of the two metallic layers in accurate register relationship as they can possibly greatly influence the resulting optical properties. Optically readily detectable orientation in accurate register relationship of the two metallic layers with each other can also be used itself directly as a security feature because reconstruction of that exact orientation in accurate register relationship is difficult and often complicated and expensive. With the previously known processes however, a film element with metallic layers which are oriented in as accurate register relationship with each other as possible and which in particular are differently structured can be implemented only with difficulty: if for example to manufacture such a film element, in a first production step, a first metallic layer is structured by means of a photoresist and, after some intermediate steps (application of further layers), in a second production step a second metallic layer is structured by means of a photoresist, registration of the second exposure process in relation to the structured first metallic layer is only possible with difficulty and involves major registration inaccuracies. In addition it has been found that the film body is admittedly only slightly but unpredictably distorted due to the processing steps which take place between the exposure processes so that for that reason also perfect structuring in accurate register relationship of the second metallic layer with the first metallic layer is unsuccessful with that procedure.